It is proposed to continue our work on the purification of UDP-G1c dehydrogenase from E. coli and from Periplaneta americana with the view of conducting studies on the nature of their active sites along the lines already pursued in the case of UDP-G1c dehydrogenase from beef liver and histidinol dehydrogenase from beef liver and histidinol dehydrogenase from S. typhimurium (J. Biol. Chem. 254, 11399 (1979)). In addition it is planned to investigate what aspect of the chemical structure of the Periplaneta-enzyme causes it to differ so greatly in properties from the mammalian and E. coli enzymes. Finally, it is planned to conduct a survey of sources of UDP-G1c in the biosphere, paying particular attention to the insects.